Summary The null layer (Nullschicht), identical with the layer of maximum wind in the upper troposphere, inverts the large scale vertical motions in the atmosphere. The lifting motion in a high reaching low pressure system ends in the null layer, whereas ascending motion above the null layer exists — and vice versa in a high pressure system. The null layer is the domain of the maximum of non-gradientic mass flow from low to high pressure (null layer effect). Applied to the theory of the general circulation of the atmosphere the null layer effect explains the mass flow aloft from the polar zones to the subtropic latitudes, demanded by almost all hypotheses of the general circulation. —It can be shown that a persistent layer of minimum winds has to be a null layer; a persistent layer of minimum winds represents a null layer of 2nd kind, which inverts the vertical motions too; but in this case the non-gradientic mass flow is directed from high to low pressure. There are evidences for the existence of a null layer of 3rd kind with calm and no mass flow between high and low pressure and no vertical motion. This null layer of third kind separates two atmospheric regions with vertical motions independent from each other. All three kinds of null layers have great importance with regard to the general circulation of the atmosphere.